1. Field of Invention
This invention relates to a circuit board and to an electrical connection box containing such a circuit board, e.g. an electrical connection box for use in an automobile or other vehicle. The invention also relates to a method of making such a circuit board.
2. Description of Related Art
To form a circuit board constituting the interior circuit of an electrical connection box, e.g. a junction box for an automobile and the like, there has conventionally been used a pressure welding system of wiring a wire, such as a single core wire or the like, along a circuit on an insulation board and connecting a pressure welding terminal on said wire by pressure welding. It is also known to use bus bars formed by stamping an electro-conductive metal plate into a circuit board shape.
When a pressure welding system is used for the formation of an interior circuit, circuits accommodated in an electrical connection box have recently increased in accordance with a large increase of electric parts to be connected. Since the shape of an insulation board where an electric wire is wired in the pressure welding system becomes complicated, problems occur such that the wiring work and the processing of an insulation board require a long time, resulting in increased production costs.
Further, when bus bars are used as an interior circuit, a mold for stamping must be made in accordance with the circuit. As a result, the alteration of a circuit cannot be easily carried out and the costs of preparation of a mold are high. Further, because a lot of residual parts are not used after stamping, the yield of the electro-conductive metal plate is poor, which also raises costs. For example, if seven or eight sheets of bus bars were arranged in multi-layer lamination with insulation boards between them, the cost is high, because of a sharp increase of the number of circuits accommodated in the inside of an electrical connection box.
A circuit board 2 for the interior of an electric connection box, shown in present FIGS. 7(A) and 7(B), is proposed in JP-A-56-130989, in view of the above problems. Insulation sheets 1a, 1b are laminated on both sides of an electro-conductive member 3, which is made in a lattice shape by stamping out the removed parts 3a of an electro-conductive metal plate. The circuit is formed by cutting the unwanted connection points 3b. Wiring is connected to the electro-conductive member 3 to make connection with exterior circuits. Since the circuit is formed by cutting the points 3b, variation of the circuit is easily achieved. However, since the lattice-shape is formed by stamping and there are a lot of the removed parts 3a, there remains the problem that the yield of the electro-conductive metal plate is not improved.
The present invention has as a first object to reduce the cost related to forming the interior circuit. Another object is to permit easy variation of a circuit. A third object is to design a cost reduction by easily forming insulation materials which lie between the third bus bars.
In a first aspect of the invention, a circuit board is provided having an insulation board with first and second opposite main faces. A plurality of first strip bus bars are arranged on the first main face. The first strip bus bars extend in parallel in a first direction. A plurality of second strip bus bars are arranged on the second main face. The second strip bus bars extend in parallel in a second direction crossing the first strip bus bar extending in the first direction, whereby, as seen in plan view, on one of the main faces there is an array of crossing points of the first and second bus bars. The insulation board has a plurality of holes through it at a plurality of the crossing points. The mutually crossing bus bars are bent each towards each other at the holes and mutually joined through the board to establish electrical connection between them, whereby a predetermined wiring pattern is obtained.
Preferably, at the holes the bus bars are joined by welding, but other joining methods are possible. Resistance welding is most preferred.
Preferably the first bus bars are located in grooves in the first main face of the insulation board, and the second bus bars are located in grooves in the second main face.
Suitably at the holes, the thickness of each of the mutually crossing bus bars in the direction of the insulation board is reduced, compared with the thickness of adjacent portions, by 15 to 25%. In the manufacture of the circuit board, this thickness reduction is accompanied by elongating the bus bar via stretching, to provide the bent portion. This can avoid disturbance of the ends of the bus bars.
A second aspect of the invention provides a method of making a circuit board, comprising the steps of:
(i) providing an insulation board having first and second opposite main faces and a plurality of holes at locations through which electrical connection is made through the board;
(ii) locating a plurality of first bus bars on the first main face extending in parallel in a first direction;
(iii) locating a plurality of second bus bars on the second main face extending in parallel in a second direction crossing the first direction, whereby as seen in plan view on one of the main faces there is an array of crossing points of the bus bars, a plurality of said crossing points coinciding with said holes;
(iv) providing each of the mutually crossing pair of the bus bars at the position of each of the holes with a portion bent towards the other bus bar of the pair;
(v) joining the mutually crossing pair of bus bars at said holes to establish electrical connection between them.
In this method, step (iv) is preferably performed to provide the bent portions at the appropriate positions, before locating the bus bars on the insulation board. Preferably, during step (iv), at least one of said first bus bars and said second bus bars are joined at opposite ends thereof to a pair of carrier members which maintain their relative positions.
Prior to the joining step (v), one of the bent portions may have a protrusion directed towards the other of said mutually crossing pair of bus bars.
Within the invention the use of material of the bus bars can be efficient, so that the yield of the material can be improved. Further, stamping by a mold which has been specifically designed for the individual circuit required is unnecessary. Therefore the cost for formation of the circuit board can be greatly reduced.
The bus bars respectively arranged in parallel in the two directions, which are typically orthogonal, may have a nominal thickness, in the direction of the insulation board, in the range of 0.5 mm to 1.0 mm. Both ends thereof may be linked with carriers, and the carriers are cut to be removed after the bent parts are joined, e.g. resistance-welded.
After the bus bars of the two directions are assembled on the insulation board, portions of them which are unnecessary in the circuit may be cut, after joining of the upper and lower bent parts, to form the requisite circuit. It is possible to use standard sets of the bus bars for both of the two directions, to simplify and reduce cost.
Further, the pitches (spacing) of the strip bus bars can be selected to correspond with the spacings of terminals of exterior components, such as a connector, a fuse and a relay. For example, some of the bus bars arranged in parallel in one direction may correspond with the terminal pitch of a fuse, while others may correspond with the terminal pitch of a relay. Some of the bus bars arranged in the second direction may correspond with the small pitch of a connector terminal hole, while others may correspond with a middle-size pitch, and the remainder may correspond with a large pitch.
Thus, tabs connected with these bus bars can be directly connected with the connector, the fuse and the relay, etc.
Further, the present invention provides an electric connection box including the above circuit board. The circuit board of the above-described construction may be arranged as a single layer in the electric connection box, or a plural number of circuit boards may be further arranged by lamination through insulation boards.